This application claims priority from Japanese application 024357/2002, filed Jan. 31, 2002.
This invention relates to a tensioner lever for maintaining tension in a flexible, circulating, power transmission medium such as a chain or belt used to transmit power from a driving sprocket or pulley to one or more driven sprockets or pulleys.
As shown in FIG. 9, a chain or belt transmission device for valve timing in an internal combustion engine, or for transmitting rotational power in another drive mechanism, includes a chain or belt C, which transmits power from a driving sprocket or pulley S1 to one or more driven sprockets or pulleys S2. The transmission includes a pivotally mounted, movable, sliding contact guide Ga, which cooperates with a tensioner, and a fixed sliding contact guide Gb. The movable guide and the fixed guide are attached to a frame E of the engine or other drive mechanism by suitable pins P or by bolts, or similar mountings. The movable guide Ga cooperates with a tensioner T, and makes sliding contact with the chain or belt C, controlling tension therein. The fixed guide Gb prevents vibration of the chain or belt both in the plane of its traveling path (which is usually vertical), and in the transverse direction.
FIG. 10 shows a movable guide 500, as disclosed in the specification of Japanese patent application No. 2000-382798. The guide comprises a guide body 510, which includes a shoe on the surface of which a traveling chain slides. The guide body also includes a plate-receiving portion 512 on the back of the shoe 511. This plate-receiving portion extends along the longitudinal direction of the guide, and the shoe and plate-receiving portion are integrally molded as a unit from a synthetic resin. A reinforcing plate 520, for reinforcing the guide body 510, is fitted into a slot 512a formed along an edge of the plate-receiving portion 512 and extending along the longitudinal direction of the guide.
A mounting hole 512b is provided in a boss 512d formed on the guide body 510 adjacent an end thereof, for pivotally mounting the guide on a mounting surface of an engine by means of a pivot such as a mounting pin P (FIG. 9) or the like. A hole 521 in the reinforcing plate 520. A tensioner contact portion 512c is provided adjacent the other end of the guide for engagement with the plunger of a tensioner T (FIG. 9), mounted on the frame of engine E.
The conventional movable guide requires a tensioner T mounted on a mounting surface of the engine frame as a separate member. Moreover, the tensioner T incorporates a complicated mechanical or hydraulic plunger-operating mechanism typically having a number of parts, and contributes to the overall weight of the tensioning mechanism, and requires a significant amount of mounting space. Contact between the guide and the plunger of the tensioner also produces contact noise and vibration noise.
Accordingly, objects of the invention are to solve the above-mentioned problems of the prior art, and to provide a tensioner lever which promotes stable and quiet operation of a flexible transmission medium, which obviates the use of a separate tensioner, which is compact in size, and which contributes to a reduction in the overall cost of a transmission device.
The tensioner lever in accordance with the invention comprises a synthetic resin lever body having an elongated shoe. The shoe has a surface for sliding engagement with a transmission medium. A spring-receiving portion is provided on the back side of the shoe, and extends along the longitudinal direction of the shoe. The spring-receiving portion has a slot, also extending along the longitudinal direction of the shoe and having an opening facing away from the shoe. A laminated sheet spring is fitted into the slot. A shaft fixed to a mounting frame is received in a mounting hole in the lever body, and the lever body is pivotable about the axis of the shaft. A proximal end of the spring is received and held in a groove formed in the shaft and extending in the axial direction. Consequently, the spring can be placed under strain by pivoting the lever about the shaft axis from a position in which the spring is relaxed, so that a reaction force exerted by the spring on the lever body can cause the lever to exert a tensioning force on a power transmission medium engaged with the surface of the shoe.
In a preferred embodiment a plurality of spring-dislodgement-preventing hooks are disposed on the spring-receiving portion of the lever at intervals along the longitudinal direction to hold the laminated sheet spring in the slot.
The materials of the synthetic resin lever bodies in the invention are not especially limited. However engineering plastics having superior wear resistance and lubricating properties, such as nylon 6, nylon 66, nylon 46, all aromatic nylons and the like are preferred, since the lever body has a surface functioning as a shoe, on which a transmission medium such as a chain, belt or the like slides. Where bending rigidity, toughness, or strength are required fiber-reinforced plastics are preferred.
The materials of the laminated sheet spring are likewise not especially limited, provided that they exhibit spring properties. Iron-based metals, or non-ferrous metals such as aluminum, magnesium, titanium and the like, can be used. The proximal end of the laminated spring is preferably in the form of a spiral, but other shapes may be used so long as the proximal end can be locked onto a groove in the pivot shaft.
The tensioner lever suppresses vibration in the traveling direction of the transmitting medium as well as widthwise vibration, and the synthetic resin lever body is uniformly supported by the entire laminated sheet spring with respect to the synthetic resin lever body without being biased in the longitudinal direction or in the direction of the width of the lever.
The locking of the spring into the spring locking groove of the pivot shaft allows the spring to exert a tensioning force on the shoe, pushing it against the transmission medium. Accordingly, the tensioner lever applies tension, avoiding loosening of the transmission medium, and thereby ensuring reliable power transmission.
The spring-dislodgement-preventing hooks disposed along the longitudinal direction of the lever hold the laminated sheet spring. Accordingly, spring is prevented from becoming dislodged from the tensioner lever, yet the tensioner lever is able to absorb stress in its longitudinal direction.